1. Field of the Invention
The present invention relates to the drilling of oil and gas wells. In another aspect, the present invention relates to systems and methods for drilling well bores and evaluating subsurface zones of interest as the well bores are drilled into such zones. In even another aspect, the present invention relates to monitoring the operability of test equipment during the drilling process.
2. Description of the Related Art
It is well known in the subterranean well drilling and completion arts to perform tests on formations intersected by a wellbore. Such tests are typically performed in order to determine geological and other physical properties of the formations and fluids contained therein. For example, by making appropriate measurements, a formation's permeability and porosity, and the fluid's resistivity, temperature, pressure, and bubble point may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed.
It is of considerable economic importance for tests such as those described hereinabove to be performed as soon as possible after the formation has been intersected by the wellbore. Early evaluation of the potential for profitable recovery of the fluid contained therein is very desirable. For example, such early evaluation enables completion operations to be planned more efficiently. In addition, it has been found that more accurate and useful information can be obtained if testing occurs as soon as possible after penetration of the formation.
As time passes after drilling, mud invasion and filter cake buildup may occur, both of which may adversely affect testing. Mud invasion occurs when formation fluids are displaced by drilling mud or mud filtrate. When invasion occurs, it may become impossible to obtain a representative sample of formation fluids or at a minimum, the duration of the sampling period must be increased to first remove the drilling fluid and then obtain a representative sample of formation fluids.
Similarly, as drilling fluid enters the surface of the wellbore in a fluid permeable zone and leaves its suspended solids on the wellbore surface, filter cake buildup occurs. The filter cakes act as a region of reduced permeability adjacent to the wellbore. Thus, once filter cakes have formed, the accuracy of reservoir pressure measurements decrease, affecting the calculations for permeability and produceability of the formation. Where the early evaluation is actually accomplished during drilling operations within the well, the drilling operations may also be more efficiently performed, since results of the early evaluation may then be used to adjust parameters of the drilling operations. In this respect, it is known in the art to interconnect formation testing equipment with a drill string so that, as the wellbore is being drilled, and without removing the drill string from the wellbore, formations intersected by the wellbore may be periodically tested.
In typical formation testing equipment suitable for interconnection with a drill string during drilling operations, various devices or systems are provided for isolating a formation from the remainder of the wellbore, drawing fluid from the formation, and measuring physical properties of the fluid and the formation. Unfortunately, due to the constraints imposed by the necessity of interconnecting the equipment with the drill string, typical formation testing equipment is not suitable for use in these circumstances.
Typical formation testing equipment is unsuitable for use while interconnected with a drill string because they encounter harsh conditions in the wellbore during the drilling process that can age and degrade the formation testing equipement before and during the testing process. These harsh conditions include vibration from the drill bit, exposure to drilling mud and formation fluids, hydraulic forces of the circulating drilling mud, and scraping of the formation testing equipment against the sides of the wellbore.
Drill strings can extend thousands of feet underground. Testing equipment inserted with the drill string into the wellbore can therefore be at great distances from the earth's surface (surface). Therefore, testing equipment added to the drill string at the surface is often in the wellbore for days during the drilling process before reaching geologic formations to be tested. Also if there is a malfunction in testing equipment, removing the equipment from a well bore for repair can take a long time.
To determine the functional status or “health” of formation testing equipment designed to be used during the drilling process, one technique is to deploy and operate the testing equipment at time intervals prior to reaching formations to be tested. These early test equipment deployments to evaluate their status can expose that equipment to greater degradation in the harsh wellbore environment than without early deployment. It is well known in the art of logging-while-drilling (LWD) how to communicate from the surface to formation testing equipment in the wellbore. Such testing equipment can be turned on and off from the surface and data collected by the testing equipment can be communicated to the surface. A common method of communication between testing equipment in the wellbore and the surface is through pressure pulses in the drilling mud circulating between the testing equipment and the surface.
Another problem faced using formation test equipment on a drill string far down a wellbore is to ensure that a series of steps in a test sequence are carried out in the proper sequence at the proper time. Communication from the earth's surface to formation testing equipment far down a well by drilling mud pulse code can take a relatively long time. Also, mud pulse communication can be confused by other equipment-caused pulses and vibrations in the drilling mud column between the down-hole testing equipment and the earth's surface.
However, in spite of the above advancements, there still exists a need in the art for apparatus and methods for a way to monitor the functional status or health of the formation testing equipment prior to its use without deploying the system.
There is another need in the art for apparatus and methods for identifying early component failures in the formation testing equipment that can cause subsequent component failures that hide early precipitating failures, which do not suffer from the disadvantages of the prior art apparatus and methods. There is even another need in the art for apparatus and methods for accomplishing test sequences by formation testing equipment down-hole automatically upon an initiating signal from the earth's surface.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.